Some major search engines suck as google are very nasty about some of these SEO tricks and put them under spam. For example, hidden texts (the ones that have the same font color as the background)are treated as spam by google.
There are others SEO "tricks" that google and other search engines treat them as spam.
Once they do treat your site as spam, you can loose your ranking and possibly the traffic that the ranking brought to your site. You may also get deleted from google db.
So be very careful which SEO "trick you use.
You can read more on it by searching google.